The present invention relates generally to the fabrication of semiconductor materials, and, more particularly, to a new fabrication configuration having an epitaxial material grown laterally in a trench and a method for producing same.
A building block of many electronic devices such as diodes, transistors, and lasers is the p-n junction. The p-n junction, or active region, is typically formed from epitaxial growth material, which is in turn grown on a substrate. The growth material can be referred to as semiconductor material. The semiconductor material is typically fabricated by growing an epitaxial layer of a chosen material upon a substrate material. The substrate material may be, and frequently is, of a different composition than the material used to grow the epitaxial layer.
The epitaxial layer is typically a thin single crystalline film that is deposited upon a crystalline substrate. The epitaxial layer is typically deposited so that the crystal lattice structure of the epitaxial layer closely matches the crystal lattice structure of the substrate. When there is a significant mismatch between the lattice structure of the substrate and the epitaxial layer, a large number of defects, or dislocations, can result. Dislocations manifest in the form of imperfections in the crystal structure and can result in high optical loss, low optical efficiency, non uniform quantum wells in the active region, or the reduction of the electrical quality of the material, thus preventing the material from being used to fabricate certain devices, such as lasers and transistor structures. A largely dislocation-free material is desired for these highly critical devices.
Dislocations are typical when trying to grow an epitaxial layer over a substrate having a different lattice structure. Dislocation densities on the order of 107 to 109 dislocations per square centimeter (cm2) can be common and result in poor semiconductor material that is unusable for certain critical applications.
Dislocation density can be reduced by adding a mask layer over the substrate material prior to growing the epitaxial layer. When the epitaxial layer is then grown over the mask, the epitaxial layer grows laterally, resulting in a reduced dislocation density being present in the portion of the epitaxial layer that resides over the mask. Because the dislocations tend to propagate vertically, the vertically grown material present in the unmasked region of a wafer will be of higher dislocation density as the defects will continue to propagate throughout the layer.
Furthermore, multiple layers of masking material having multiple layers of epitaxial growth may further reduce the dislocation density. While the growing of multiple epitaxial layers over mask layers has some benefit, a drawback is that the mask layer adds cost, complexity, and can add contamination to the epitaxial growth material. Successive iterations may yield low dislocation density material over the entire wafer. It would be desirable to grow the material in a manner in which the low dislocation density material is present over the entire wafer in a single growth sequence.
Thus, an unaddressed need exists in the industry for a simplified method for developing a quantity of high quality, low dislocation density material, which covers the entire surface of a wafer, in an epitaxial layer grown over a lattice mismatched substrate.
The invention provides an epitaxial material grown laterally in a trench and a method for producing same. Although not limited to these particular applications, the material and method for producing it are particularly suited for fabrication of high quality GaN material system epitaxial layers over a sapphire substrate. The GaN material system can include members of the Group III-V family including, but not limited to, gallium nitride (GaN), indium gallium nitride (InGaN), indium nitride (InN), aluminum gallium nitride (AlGaN), aluminum nitride (AlN), aluminum indium gallium nitride (AlInGaN), gallium arsenide nitride (GaAsN), indium gallium arsenide nitride (InGaAsN), aluminum gallium arsenide nitride (AlGaAsN), gallium phosphide nitride (GaPN), indium gallium phosphide nitride (InGaPN), aluminum gallium phosphide nitride (AlGaPN), etc.
The present invention can be conceptualized as providing a method for growing a low dislocation density material comprising the following steps. First, a trench is formed in a substrate. Alternatively, an epitaxial layer is grown over a substrate and a trench is formed therein. The trench is formed preferably by etching the substrate or the first epitaxial layer. An epitaxial lateral growth layer is then grown in the trench, the growth layer originating from the side walls of the trench. Illustratively the epitaxial lateral growth layer can partially fill, completely fill, or overflow the trench. It is also possible to apply a mask layer, which can be either an insulating layer or a conducting layer, at the bottom of the trench, over the top of the first epitaxial layer, or any combination thereof.
In an alternate embodiment the epitaxial lateral growth layer can be grown from a single wall of the trench laterally across the trench, and eventually filling and overflowing the trench. In addition a device having a p-n junction, or active region, can be grown in the epitaxial lateral growth layer.
In architecture, when employed in connection with the fabrication of a low dislocation density material, the aforementioned method for multiple lateral growth of an epitaxial layer including the forming of a trench in the epitaxial material results in a low dislocation density material as follows.
A low dislocation density material system comprises a substrate, or alternatively, a first epitaxial layer over a substrate. A trench is formed, preferably by etching, in the substrate or the first epitaxial layer. An epitaxial lateral growth layer is then grown in the trench, the growth layer extending from the side walls of the trench. The material can further comprise a mask layer, the mask layer being either insulating material or conducting material and applied to the bottom of the trench, over the first epitaxial layer, or any combination thereof. The mask material is designed to further control and define the growth pattern of the epitaxial lateral growth layer. Furthermore, one side wall of the trench can be coated with the mask layer, and the epitaxial lateral growth layer can then be grown from the opposing side wall of the trench. When grown from a side wall of the trench the epitaxial lateral growth layer can have a p-n junction, or active region, formed therein.
The invention has numerous advantages, a few which are delineated, hereafter, as merely examples.
An advantage of the invention is that it increases the yield of high quality, low dislocation density material in an epitaxial layer grown over a substrate.
Another advantage of the invention is that it reduces the amount of optical loss in the epitaxial layer of a semiconductor material.
Another advantage of the invention is that it increases the optical efficiency in the epitaxial layer of a semiconductor material.
Another advantage of the invention is that it improves the electrical performance of the material forming the epitaxial layer of a semiconductor.
Another advantage of the invention is that contamination arising from the use of a mask can be reduced or eliminated.
Another advantage of the invention is that it is simple in design and easily implemented on a mass scale for commercial production.
Other features and advantages of the invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. These additional features and advantages are intended to be included herein within the scope of the present invention.